In this constantly-meshing type multistage transmission, either of the driving gears or the driven gears are fixed to one gear shaft, the other are supported on the other gear shaft in a manner turnable relative to the other gear shaft, and speed shift is executed by selectively changing over the turnable gear, which is to be engaged with the other gear shaft via an engagement means.
A document (patent document 1) of the present applicant discloses a mechanism using a swingable lever operated by a cam member for the engagement of the turnable gear with a gear shaft.